n = int(input())
c = list(input())
print(c[:c.count("R")].count("W")) n = int(input()) n int(input()) int input() input c = list(input()) c list(input()) list input() input print(c[:c.count("R")].count("W")) print c[:c.count("R")].count("W") [:c.count("R")].count [:c.count("R")] c :c.count("R") c.count("R") c.count c count "R" count "W" c = list(input()) list(input()) c n = int(input()) int(input()) n
n = int(input())
c = list(input())
print(c[:c.count("R")].count("W"))